Solutions for Home Work 10

1. What is the queue length in buffer 1 at time 1.5 msec?
   At time 2.5 msec? At time 3.5 msec? At time 5.25 msec?
   At time 5.75 msec?


   Queue length in buffer 1 at time 1.5msec is 1 (frame 4 is the only one in queue waiting to be serviced,
						  frame 3 is in service)

   				    2.5msec is 0 (frame 4 is the only frame in the buffer but it is being serviced)

				    3.5msec is 0 (no frames in buffer)

			            5.25msec is 0 (buffer is still empty)

				    5.75msec is 0 (frame 5 is in the buffer but is being serviced)

2. If this simulation continues ``forever'', what fraction of 
   the time is the interface between buffer 1 and link 1 busy?
   What fraction of the time is it idle?


   The interface between buffer 1 and link 1 is busy for the interval when the frames are being given to the link. 
From the simulation output, we can see that the interface is busy from 0 - 3msec in which the frames 2, 3 and 4 are sent to 
the link and then it is idle till it receives an ack for frame 2 at 5.5msec. After which it again becomes busy for another 3msec 
and becomes idle. If the simulator has to run forever the pattern will keep on repeating as there are no loss and damage in the link.

Thus, the fraction of the time the interface is busy is 3/5.5 = 0.5454
and the fraction of the time the interface is idle is 2.5/5.5 = 0.4545

3. If this simulation continues ``forever'', what is the ``goodput'' of the system? (In frames / sec).

   From the simulation output, we can see that for every 5.5msec, 3 frames are sent out from the source. Since, there is no loss or damage 
in the link(probability of loss and damage is zero), all these frames will arrive intact in the destination. 

So, the goodput of the system is: (3 / 5.5) = 0.5454 frames/msec.